1. Field of the Invention
The present invention provides stabilized and/or dense L-amino acid nutrient compositions. Such stabilized and/or dense L-amino acid nutrient compositions may be prepared by using oligopeptides whose molecules contain at least one L-amino acid residue of some specific L-amino acids.
2. Discussion of the Background
When patients cannot orally take, or can take orally but in an insufficient amount of, amino acids or protein in various diseases or in preoperative or postoperative stage, etc. in spite of necessity to take them, L-amino acid nutrient compositions whose main ingredients are L-amino acids, e.g., L-amino acid infusion solutions for intravenous administration (referred to hereinafter as "amino acid infusion solutions") have been widely utilized for the purpose of nutrient supplementation.
In general, however, amino acid infusion solutions tend to form degradation products with the passage of time and color to yellow. Therefore, for the purpose of preventing coloration, etc., i.e., as stabilizers, there have been hitherto used inorganic salts of sulfurous acid or pyrosulfurous acid such as sodium hydrogensulfite, potassium hydrogensulfite, sodium sulfite, potassium sulfite, sodium pyrosulfite, potassium pyrosulfite, etc. A method for stabilization using sulfurous acid salts of basic amino acids is also disclosed (Japanese Patent Application Laid-Open No. 49-102831). These hydrogensulfites or sulfites are very effective for preventing coloration of amino acid infusion solutions. Among them, hydrogensulfites are superior.
However, it is known that the hydrogensulfites and sulfites react with amino acids. They are very reactive, in particular, with cystine, methionine or tryptophan. For example, these salts react with cystine to cleave the disulfide bond and give cysteine thiosulfate. Furthermore, the salts react with methionine in the presence of oxygen to form methionine sulfoxide. The salts cause an extremely complicated reaction with tryptophan and the major reaction products are highly reactive formylkynurenine, 2,3-dioxyindolealanine, etc. As such, these salts are effective for apparent prevention of coloration of amino acid infusion solutions but give reaction products which are harmful to the living body. Moreover, the hydrogensulfites or sulfites react with protein to cleave disulfide bond or bind to protein itself when they are taken into the living body. Furthermore, the salts also react with nucleic acid bases or other compounds in the living body and are known to have a potent mutagenecity.
Accordingly, it is not preferred to use the hydrogensulfites or sulfites as stabilizers for amino acid infusion solutions. However, no stabilizers better than these salts are known so that the prior art cannot help using the salts in a trace amount under the actual situation.
It has been now found that the prime cause of instability such as coloration, etc. of amino acid infusion solutions is attributable to L-tryptophan (Trp) and the coloration is proportional to the concentration of Trp in amino acid infusion solutions. Trp is one of essential amino acids. It is known that Trp greatly affects protein synthesis in liver and it has been a demand to increase the Trp concentration in an amino acid infusion solution. As already stated, however, there have been serious problems in preparation of amino acid infusion solutions that an increase in the Trp concentration results in increased coloration and the like.
A first problem to be solved by the present invention is, under the above-described prior art, to provide stable, L-amino acid-containing nutrient aqueous compositions which contain the Trp ingredient in a desirable amount but no stabilizers such as hydrogensulfites or sulfites conventionally used.
On the other hand, recently, since researches on the amino acid metabolism under the sick conditions have been promoted and hence the roles of the various amino acids under the sick conditions have been made clear, the stream of the development of the amino acid infusion solutions is divided into two directions, that is, the development of amino acid infusion solutions according to the respective sick conditions taking the therapeutic aspect into consideration on one hand and the development of general-purpose amino acid infusion solutions for correcting the nutrient characteristics relatively common to the various sick conditions on the other hand.
Among L-amino acids used for amino acid infusion solutions, L-tyrosine (Tyr) has been proven essential for liver diseases, uremia, immature infants, newborns, etc. Inter alia, with uremia patients, especially Tyr indicates a low level. This is due to that the activity of L-phenylalanine (Phe) hydroxylase is low and thus that the production of Tyr from Phe is inadequate. The decrease in the protein synthesis due to the Tyr deficiency has been recognized to extremely lower the nutrient conditions of the patient. Further, since Tyr is a precursor to catecholamine, it is also indicated that if this is inadequate, various neurosis signs are brought about, and with these patients, Tyr has been gradually taking the position as an essential amino acid. For that reason, it is the present situation that an amino acid infusion solution in which Tyr is formulated so as to adapt to these sick conditions has been sought. However, the solubility of Tyr in water is merely 0.045 g/dl at 25.degree. C., and it is difficult to freely formulate a necessary amount thereof as an ingredient for infusion solution.
As regards the formulation of Tyr in infusion solutions, compositions based on nutrient formulations for healthy humans have heretofore been used, for example, those based on amino acid compositions of human milk or the whole egg according to the report of FAO special committee, 1957, etc. However, as described earlier, with healthy humans Tyr can be synthesized in an adequate amount from Phe, but such synthesis is impossible with certain sick conditions and thus Tyr is positioned as an essential amino acid. Therefore, it is evident that the nutrient formulation for these patients is different from the nutrient formulation for healthy humans.
The formulation for sick conditions taking this into consideration is disclosed in Japanese Patent Application Laid-Open No. 59-16187, where it is indicated that favorable results are obtained when Tyr is contained in the range of 1/12- 1/17 based on Phe and at a concentration of 0.45-0.55 g/l. However, according to the research on the metabolism of the ingested essential amino acid Phe in vivo, it has been discovered that 50-70 % of the ingested Phe has been converted into Tyr. It is thought that Phe must be present at a concentration of 5.0-10.0 g/l in an ordinary amino acid infusion solution. Even by simple calculation considering the conversion rate described above, it may be presumed that the part 2.5-7.0 g/l of Phe in the formulation must be replaced by Tyr under sick conditions. When this is taken into consideration, the formulation presented in Japanese Patent Application Laid-Open No. 59-16187 has been designed in the range of Tyr solubility, and it seems uncertain that the sick conditions are well considered. On the other hand, no amino acid infusion solutions containing such a high concentration of Tyr have been known.
In the meantime, several methods for increasing the concentration of Tyr have been proposed. Japanese Patent Application Laid-Open No. 56-8312 discloses a method which utilizes peptides such as L-alanyl-L-tyrosine, L-arginyl-L-tyrosine, L-tyrosyl-L-arginine etc., Japanese Patent Application Laid-Open No. 61-247354 discloses glycyl-L-tyrosine and L-alanyl-L-tyrosine and Japanese Patent Application Laid-Open No.62-151156 discloses L-aspartyl-L-tyrosine. However, any of these seems uncertain that the formulations of Tyr are fully studied.
A second problem to be solved by the present invention is, under the above-described prior art, to present an amino acid nutrient infusion composition of a new formulation which contains sparingly soluble tyrosine in an amount necessary at a ratio achieving the purpose without being subject to the pharmaceutical restrictions and also can exert an excellent nutrient effect to the various intended diseases.
As has been discussed earlier, recently, studies on amino acid metabolism under morbid conditions have been advanced, and have revealed the roles of various amino acids under pathological conditions, as a result of which the trend of developing amino acid infusion solutions is divided into two directions: one is to pursue amino acid infusion solutions used in respective diseases laying a stress on therapy and another is to pursue all-purpose amino acid infusion solutions with an attempt to correct nutritious imbalance relatively common to various morbid conditions.
With respect to the branched chain L-amino acids (BCAA) of L-leucine (Leu), L-isoleucine (Ile) and L-valine (Val) among L-amino acids used in amino acid infusion solutions, their sitological significance has been clarified over wide areas including application to surgical seizures, hepatic insufficiency, renal insufficiency, septicemia, premature infant, etc. For development of infusion solutions in either direction described above, attention has been drawn to these amino acids as one of the most important amino acid group. It is known that unlike other amino acids, the branched chain L-amino acids are metabolized mainly in tissues other than liver, and,in particular, Leu has an activity to accelerate synthesis of muscular protein and prevent its decomposition. It is also known that when the branched chain amino acids have been administered to humans in relatively large quantities, their blood concentration does not increase very much and an influence on amino acid distribution in blood is small. Such findings have increased a demand for highly dense amino acid infusion solutions for administration via the central vein in which a rate of the branched chain amin acids to the total L-amino acids (BCAA/TAA) is increased.
However, solubilities of Leu, Ile and Val in water at 25.degree. C. are 2.19, 4.12 and 8.85 g/dl, respectively. When other amino acids are co-present, any of the solubilities decreases. For example, a mixture of Leu and Ile in almost equimolar amounts has a solubility of approximately 2.2 g/dl and a mixture of Leu, Ile, Val, L-methionine (Met) and Phe has a solubility of approximately 4.5 g/dl. Thus, when it is wished to raise a concentration of the branched chain amino acids, a concentration of other L-amino acids should be extremely reduced so that unbalanced distribution of L-amino acids in blood is caused. Accordingly, its application has been limited to special cases for a patient with hepatic encephalosis, etc. That is, it has been difficult to prepare highly concentrated amino acid infusion solutions containing other L-amino acids in a well-balanced state to be suited for any desired purpose, while increasing a ratio of the branched chain amino acids to the total L-amino acids.
Some proposals have already been made to increase the concentration of the L-amino acid content using water soluble oligopeptides, though the proposals don't pay attention particularly to the branched chain amino acids. For example, in Japanese Patent Application Laid-Open No. 56-140923, there is disclosed a method using at least two oligopeptides containing glycine residue as the N-terminal. According to this method, however, a proportion of the specific amino acid, glycine (Gly), becomes extremely high to cause imblanced distribution of L-amino acids in blood, which is not preferable. Furthermore, in Japanese Patent Application Laid-Open No. 61-247354, there is disclosed a method using oligopeptide(s) containing a glycine residue as the N-terminal in combination with oligopeptide(s) containing as the N-terminal a residue from at least one amino acid selected from the group consisting of Ala, L-arginine (Arg) and L-lysine (Lys). However, as is demonstrated in the Laid-Open Applications, an increased concentration of the branched chain amino acids is accompanied by a high concentration of Gly, Ala, Arg or Lys. As a result, it is difficult to provide sitologically preferred compositions.
The present invention aims at providing highly dense amino acid infusion solutions which can exhibit excellent nutrient effect in various diseases. That is, a third problem to be solved by the present invention is, under the above-described prior art, to provide L-amino acid compositions for infusion in which a rate of the branched chain amino acid components is increased, other amino acids are formulated in a well balanced state and a high concentration can be achieved without any limitation on preparations.
Furthermore, as has been discussed above, as recent studies on amino acid metabolism under morbid conditions have been advanced, it has been desired to develop amino acid infusion solutions used for pathologic conditions such as surgical seizures, hepatic insufficiency, renal disorder, septicemia, premature infant, etc. In particular, attention has been drawn to the branched chain L-amino acids (BCAA) metabolized in organs other than liver and by enhancing a proportion of BCAA to the total L-amino acids (TAA), nutrient effects have been increased in pre-operative and post-operative stages. For treatment of some specific disease, there is known Fischer et al's composition applicable to patients with hepatic encephalosis in which the BCAA content is increased while the contents of Met, Phe and Trp are restricted; or the like.
A ratio of BCAA to be incorporated has also been studied, and, as a result, it has been found that an increased ratio of Leu is necessary for exhibiting good effects on sitological parameters. It is also known by the studies heretofore made that when a ratio of BCAA to TAA (BCAA/TAA) is 25 to 60%, good results are given. In addition, as has been stated above, even though BCAA is intravenously administered in a relatively large dose, its blood concentration does not increase so that imbalanced distribution of L-amino acids in blood does not occur. Based on these research results, it has been demanded to increase the ratio of BCAA to TAA (BCAA/TAA) and increase the concentration of BCAA more. In particular, as the complete intravenous utilizing the central veins has been advanced, an amount of water administered is limited so that a much higher concentration of an infusion solution has been demanded, as has been also stated above. However, solubilities of Leu, Ile and Val in water at 25.degree. C. are 2.19, 4.12 and 8.85 g/dl, respectively. When these amino acids are further mixed with other amino acids, any of the solubilities decreases, as has been already stated. Among them, it is difficult to increase the concentration of Leu, which is sitologically desirable. I.e., there has been a bar against the preparation of dense infusion solutions having a high concentration of BCAA in compliance with the purpose of use.
Several proposals have already been made, as has been stated above, to increase the concentration of the L-amino acid components in general (Japanese Patent Application Laid-Open No. 56-140923 and Japanese Patent Application Laid-Open No. 61-247354). However, as is demonstrated in the Laid-Open Applications, an increased concentration of BCAA is accompanied by an increased concentration of other L-amino acids, and this is not preferred.
As a result of extensive investigations, the present inventors have found that by mixing a composition mainly composed of BCAA with an ordinary amino acid infusion solution in a suitable ratio, an amino acid infusion solution suited for various specific morbid conditions can be readily obtained.
A fourth problem to be solved by the present invention is, under the above-described prior art, to provide BCAA compositions which are used for preparing amino acid infusion solutions which are free from any preparation restrictions but contain BCAA in a large ratio suited for the purpose in a necessary dose by simply adding such BCAA composition to an ordinary amino acid infusion solution when administered.